1. Field of the Invention
This invention relates generally to a speaker (or audio transducer) for reproducing bass frequencies and, more particularly, to a back to back mounted compound woofer with compression/bandpass loading.
2. Description of the Prior Art
The prior art in woofer designs is very well known and can be characterized by the quest for greater performance in ever-smaller packages. Large woofers in small boxes with very high power modifiers employing motional feedback to maintain linearity are commonly found now. If capable of good sound quality they are quite expensive and because of the extraordinary punishment delivered to the transducer to overcome the physical constraints inherent in these designs, can develop mechanical trouble and fail over time.
It should be noted that this new invention is not antagonist to these other design approaches, indeed a marriage could be quite beneficial, but that very conservatively designed transducers employing modest power amplifiers can yield exceptional results in an acceptable package size and cost.
A pair of woofer speakers or low frequency transducers, when mounted and operated as disclosed herein will exhibit a lower resonant frequency, higher sensitivity (or conversion of electrical to acoustic power), and better rejection of frequencies above its desired operating range, than would be expected, by well known calculations.
The device is very stable mechanically and because of this, unwanted or parasitic vibrations are practically non-existent. This allows use of a much more lightly constructed enclosed without extensive cross bracing than would otherwise be employed. It is also very advantageous in car applications where available mounting panels are by nature, flimsy.
A housing provides an enclosure for the compound woofer. The housing includes opposed sidewalls or side plates, each having a coaxial opening. Each of two speakers is mounted on a respective coaxial opening of a respective sidewall. Additionally, the two speakers are mounted back to back, i.e., with their magnet structures in close proximity to one another. In one embodiment, the magnet structures are coupled to one another using a flexible sealing compound such as putty. In another embodiment, the two speakers share a common unitary magnet structure. The containing volume around the speakers is made as small as physically possible by using, in one embodiment, a spiral curve member to form a substantially circular woofer housing around the speakers. The spiral curve member forms an first enclosed channel that is the main exhaust of the two woofers. A curve member together with the spiral curve member forms a primary vent for venting the woofer output. The spiral curve member and the curve member maintain an even distance between the two sidewalls and support the two sidewalls. In other embodiments, the containing volume around the speakers is minimized using a six-sided box or a tube. The box or tube housing is confined within an external enclosure. A vent connects the box or tube and the enclosure for venting the pair of speakers to the outside.